On the basis of mechanism of products existing a fixed market fullness, this paper devotes to their market diffusion mechanism by constructing a mathematical model of market diffusion of "co-existing" products, which figures out the dynamical regularity during their market diffusion. Based on its analysis the paper provides the advise to relevant enterprises on how to modulate their manufacturing size to obtain best profits. This paper employs systematical theory to approach the regularity of products proceeding market diffusion which is discriminated of single-element analysis dealt with in the proceeding relative reference.